1. Field of the Invention
The present invention relates to a photographing lens assembly applicable to mobile phone cameras or digital cameras, and more particularly, to a compact photographing lens assembly used in a mobile phone camera.
2. Description of the Prior Art
In recent years, with the popularity of mobile phone cameras, the demand for compact imaging lenses is increasing, and the sensor of a general photographing camera is none other than CCD (charge coupled device) or CMOS Sensor (Complementary Metal Oxide Semiconductor Sensor). Furthermore, as advanced semiconductor manufacturing technology has allowed the pixel size of sensors to be reduced and electronic products have become more compact and powerful, there is an increasing demand for compact imaging lenses featuring better image quality.
Generally, a conventional lens assembly for mobile phone cameras, such as the one disclosed in U.S. Pat. No. 7,145,736, is of a triplet type comprising, in order from the object side to the image side: a first lens element with positive refractive power; a second lens element with negative refractive power; and a third lens element with positive refractive power. However, the three-element lens assembly has become insufficient for a high-end imaging lens module due to the reduction in the pixel size of sensors and the increasing demand for lens assemblies featuring better image quality.
U.S. Pat. No. 7,365,920 has disclosed a four lens element assembly where the first and second lens elements are adhered by means of two glass spherical-surface lenses to form a doublet and thereby to correct the chromatic aberration. Such an arrangement of optical elements, however, has the following disadvantages: (1) the freedom of the system is curtailed due to the employment of excess number of glass spherical-surface lenses, thus the total track length of the system cannot be reduced easily; (2) the process of adhering the glass lenses together is complicated, posing difficulties in manufacture.